(a) Field of the Invention
The present invention relates to a display device and in particular, a touch detecting display device.
(b) Description of Related Art
A liquid crystal display (LCD) includes a pair of panels provided with pixel electrodes and a common electrode and a liquid crystal layer with dielectric anisotropy interposed between the panels. The pixel electrodes are arranged in a matrix and connected to switching elements such as thin film transistors (TFTs) such that they receive image data voltages row by row. Typically, the common electrode covers the entire surface of one of the two panels and it is supplied with a common voltage. A pixel electrode and corresponding portions of the common electrode, and corresponding portions of the liquid crystal layer form a liquid crystal capacitor that as well as a switching element connected thereto is a basic element of a pixel.
An LCD generates electric fields by applying voltages to pixel electrodes and a common electrode and varies the strength of the electric fields to adjust the transmittance of light passing through a liquid crystal layer, thereby displaying images.
Recently, an LCD incorporating photosensors has been developed. The photosensors sense the change of incident light caused by a touch of a finger or a stylus and provide electrical signals corresponding thereto for the LCD. The LCD determines whether and where a touch occurred based on the electrical signals. The LCD sends the information on the touch to an external device that may return image signals to the LCD, which are generated based on the information. Although the photosensors may be provided on an external device such as a touch screen panel to be attached to the LCD, it may increase the thickness and the weight of the LCD and it may make it difficult to represent minute characters or pictures.
A photosensor incorporated into an LCD may be implemented as a thin film transistor (TFT) disposed in a pixel displaying an image.
However, display signals and sensing signals may interfere with each other when the display operation and the sensing operation are simultaneously performed.
Furthermore, the photosensors are sensitive to characteristics of the external environment, such as luminance. For example, when the environment is dark, the sensing signals may be significantly affected by the display signals, and the magnitude of the sensing signals may be too small to determine a touched position.
Additionally, including photosensors in the display area may decrease the resolution of the pixels.